I think you can do it if you know him. For example: Hey Obama, do you want beer or coke? But in that case probably you would say Barack, or Hussein, depends.
If dont, reason to use the surname is to make the difference. Because could have more Barack than him, same than Kennedy instead of John or Clinton and not William or Bill. For other side, in every situation you could refer with different uses: the Honorable Barack Obama, with formality; Mr. Obama, with respect, and like that.
Normally media use President Obama because is a normalized use to refer about some thing. If you speaking about some in concret, you could say: the President Obama said... or Mr. Obama is...
So depends, you know, but full title is just for special situations, like ceremonies or whenever is neccesary to give importance the specific act
